Treatment of cultured CD34⁺ cells with Delta-1 in a fed-batch platform inhibits IL-6 cis- and trans-signaling in myeloid committed progenitor cells and reduces the production of mature inflammatory myeloid cells, which leads to depletion of inhibitory factors produced by these cells. Concomitant inhibition of mature myeloid cell production and depletion of inhibitory signals result in extensive ex vivo expansion of HSC from cultured CD34⁺ cells.